While advanced functionality of mobile devices increases with the rapid development of mobile devices, the capacity of batteries of mobile devices remains limited. For this reason, most mobile device manufacturers put more effort into increasing the use time of mobile devices rather than increasing battery capacity. In other words, most mobile device manufacturers focus more on improving battery use efficiency than increasing battery capacity.
Mobile devices typically include a low-dropout (LDO) regulator that is provided with an operating voltage from a power management IC included in the mobile device. The LDO regulator converts the operating voltage into an output voltage that is provided to a semiconductor chip of the mobile device. The LDO regulator needs to obtain a sufficient dropout voltage, i.e., a difference between an input voltage and an output voltage of the LDO regulator, in order to correctly generate the output voltage that is provided to the semiconductor chip. The LDO regulator has a feedback loop that includes an error amplifier and a power transistor. The error amplifier measures the difference between a reference voltage and the output voltage and adjusts the gate voltage of the power transistor in order to regulate the dropout voltage of the LDO regulator.
If the dropout voltage is too small, the overall feedback loop gain of the LDO regulator decreases. As a result, a large error occurs in the output voltage of the LDO regulator. However, although a sufficient dropout voltage is needed to prevent errors in the output voltage of the LDO regulator, the power efficiency of the LDO regulator decreases as the dropout voltage increases.
In some cases, a single LDO regulator is required to provide a plurality of output voltages. If a plurality of error amplifiers are used to provide the LDO regulator with a plurality of output voltages, the size of the chip that incorporates the LDO regulator and driving current may increase with the increase in the number of error amplifiers, which are undesirable effects.